This invention relates in general to ink ribbon cassettes, and in particular to ink ribbon cassettes containing a feed spool and a winding spool for use in printing applications.
Dual spool cassettes are known in the art as disclosed in U.S. Pat. No. 4,406,554. In this cassette both the feed spool and the winding spool are guided in slots in the housing. The feed spool is pressed by a spring against a roller rotatably supported in the housing. The winding spool is urged by a spring against a drive roller which is engaged by a drive shaft of the typewriter or printer. These cassettes are advantageous in that they enable automatic detection of the tape's end.
Another such ribbon cassette is shown in European Patent Application No. 122,755. In this cassette, a slide is slideably supported in the housing. Two pins project from the slide, one of which supports a feed spool, the other pin supports a winding spool. The slide is urged by a spring against a drive roll which is engaged by a drive shaft of the typewriter. This is advantageous in that the axis of the two spools are aligned and do not tilt resulting in safer operation and reduced friction.
These prior art cassettes have been satisfactory; however, they suffer from the disadvantage that the pressure of the winding spool against the drive roll varies with the spool diameter. The spring must be constructed and placed so that the minimum pressure required to drive the winding spool is guaranteed. Therefore, the pressure actually increases too much as the diameter of the winding spool increases. This results in frictional losses and high torque required from the driveshaft of the typewriter or printer. Another disadvantage is that in some of the prior art devices the two spools are not perfectly guided and tend to tilt. Accordingly, it is desireable to provide an ink ribbon cassette for two spooled cassettes which overcome the shortcomings of the prior art devices described above.